Electrical fuel burner control system and apparatus therefor



F- B. AUBERT April 22, 1952 Filed July 11, 1947 3 Sheets-Sheet 1 3ATTORNEY aw i o R. 0 a m 2 l m w m U mm mm W. d \m 3 L VE vm p? M .QF Ow1v V. B m@\e| 3 mm 2 5 h 5 2 m 4 2 E F 9 m WM U WN 4 fig d 3 r m @N A Ymm #5 om m9 g .Q Q 5m 0m cm A I" N\ E M BMM 8 Q em mm Mm F. B. AUBERTApril 22, 1952 ELECTRICAL FUEL BURNER CONTROL SYSTEM AND APPARATUSTHEREFOR 3 Sheets-Sheet 2 Filed July 11, 1947 wmu INVENTOR.

ATTORNEY F. B. AUBERT April 22, 1952 ELECTRICAL FUEL BURNER CONTROLSYSTEM AND APPARATUS THEREFOR 3 Sheets-Sheet 3 Filed July 11, 1947INVENTOR.

BY W K M) ATTORNEY Patented Apr. 22, 1952 UNITED STATES PATENT OFFICEELECTRICAL FUEL BURNER CONTROL SYSTEM ANDAPPARATUS THEREFOR 17 Claims. 1

This invention relates .to new and useful improvements in electricalfuel burner control systems and apparatus therefor.

An object of this invention is to provide a control system for fluidfuel burners having electrically operable fuel supply means andelectrically controllable ignition means.

Another object of this invention is to provide a control system havin ameans responsive to the occurrence of flame in the burner whereby theignition means may he de-energized and enere gization of the fuel supplymeans continued.

Another object of this invention is to provide a safety means for acontrol system to de-energize the fuel supply means and ignition meansupon failure of flame to occur in the burner within a predetermined timeafter initial energization of the system.

Another object is to provide a control device for automaticallysupervising the operation .of a fluid fuel burner.

Other objects of thisinvention will become apparent from time to timethrough the specification and claims as hereinafter stated.

This invention consists in the new and improved combination of parts andin their operative relationship to each other and in certain controldevices therefor, all to be more fully described hereinafter and thenovelty of which Will be particularly pointed outand distinctly claimed.

In the accompanying drawings to be taken as part of the specificationthere are clearly and fully illustrated several preferred embodiments ofthis invention in which drawings;

Figure 1 is -a diagrammatic representation of a fuel burner controlsystem utilizing a thermostatic stack switch responsive to theoccurrence of flame in the burner and operable tocontrol operation ofthe fuel supply meansgandtheignition means,

Fig. 2 is a diagrammatic'view of another form of burner controlsystem inwhich a photo-electric cell is positioned to be responsive to theoccurrence of flame inthe burner and is operable. to control theactivation of an electron tubein the system for controlling the,fuel-supplymeans and ignition means for the burner and having electrictiming means to delay functioningof the photoelectric cell'until-"theelectron tube has had time to .become adequately heated,

Fig. 3 is adetail view, of the electric timing means portion of Fig. 2in a partially operated position,

Fig. 4 is a detail .view of the electric timing means portion of Fig. 2when the control system is in a fully operated position,

Fig. 5 is a detail view of the electric timing means portion of Fig.2 insafety operation,

Fig. 6 is a diagrammatic view of another form of a burner control systemhaving 'a photoelectric cell and electron tube for controlling theoperation of a fuel supply means and ignition means for the burner,having electric timing means to prevent functioning of the systemuntilthe electron tube has had time tobecome adequately heated, and havingsafety means to deenergize the system and prevent further operation uponfailure of flame to occur in the burner within a pre-determined timeafter initial ener gization of the system and having a safety stopmember to prevent the safety means from returning to its initialposition after operation,

Fig. '7 is a detail view of a section of the system shown in Fig. 6including the safety means and is shown in an intermediate position ofoperation,

Fig. 8 is a detail view similar to Fig. 7 but shows the control systemin fully operated position, and

Fig. 9 is another detail view similar to Figs. 7 and 8 showing thesafety means in safety operatedv position.

Referring to the drawings by characters of reference, in the systemshown in Fig. 1 there is a burner I having a fan or blower 2 and a fuelsupply line 2 terminating in a nozzle. In the line 2 there is a pump lwhich is driven -by-a motor 3 which also drives the blower 2. Adjacentthe nozzle there are ignition electrodes 4.

Electrical power from a main power source is supplied to electricalconductors 5 and 6 for energization of the system. The electricalconductors 5 and 6 are shown as leading to a connection or terminalboard or panel I and connected-thereto by screws 8 and 9. The parts ofthe system are shown as beinginterconnected through the'connectionpanel 1. The elements of the'controlsystem to the right of the panel Iin the drawing are sointerconnected and interrelated-in their operatlonthat in commercial construction they-would probably be housed within acasing as an individual control device, the vconnections to the controldevice beingmade through the connection panel 1 as shown. From theconnection points 8 and 9 on the panel 1, two electrical conductors i0and H run to the primary ['2 of a transformer [Sand form a completecircuit therewith. From the secondary ['4 of the transformer l3 .aconductor l5 runs to a connection point 16 on the panel 1 from whichanother conductor I! leads to the fixed contact 18 of a roomthermostator other control 3 switch I9. The thermostat I9 has a movablecontact 29 carried by a thermo-sensitive bimetal strip or blade 2I whichis connected by a conductor 22 to a connection point 23 on the panel 1.The thermostat I9 has a compensating, heater coil 24 which is connectedby a conductor 25 from the blade 2| to a connection point 23 on theconnection panel I. A conductor 21 leads from the connection point 23 tothe coil 28 of a relay switch 29. The relay switch 29 has two fixedcontacts 39 and BI and two movable contacts 32 and 33 cooperablerespectively therewith and carried by pivoted contact arms 34 and 35respectively, the switch contacts being held in open position initiallyby a spring 35. In the initial open position of the relay switch 29, theend portion 31 of the contact arm 35 engages and holds closed through aninsulating abutment the pivoted contact-carrying arm 38 of a controlswitch 39. The control switch 39 has two fixed contacts 49 and M and hastwo movable contacts 42 and 43 cooperable respectively therewith andcarried by the arm 38. A spring 44 is connected to the contact arm 38urging it towards contact open position, the opening movement of theswitch 39 being limited by the engagement of the arm 39 with a stop 45.The contact arm 39 has an electric insulating abutment 4B thereon whichis engaged by a pivoted member 41 which is operable to continue to holdthe switch 39 closed after releasing movement of the relay switch 29.The pivoted member 41 is urged towards its initial position inengagement with the abutment 45 by a spring 48 and is limited in itsmovement in this direction by a stop member 49. The upper portion 59 ofthe pivoted member 41 is engageable with the contact-carrying arm 5! ofa switch 52, the contactcarrying arm 5I being of cantilever springconstruction and tensioned toward contact closed position. Thecontact-carrying arm 5| carries the movable contact 53 which isinitially in engagement with a fixed contact 54 of the switch 52. Thearm 5I also carries a magnet armature 55 which is attracted by apermanent magnet 55 adjacent the fixed contact 54 which is operable tohold the contacts 53 and 54 tensioned against each other so thatmovement of the switch 52 will be with a snap action. A second relayswitch 51 has a coil 58, a fixed contact 59 and a movable contact 69.The movable contact 59 of the relay switch 51 is carried by acontact-carrying arm BI and is urged towards open position by a spring62. The contact-carrying arm 9I has an electric insulating abutmentmember 63 thereon which is engageable with the pivoted member 41 andoperable to move the same out of holding engagement with abutment 49upon closingv movement of the relay switch 51. A bimetal element 34having an abutment member 65 of electric insulating material isengageable with and operable to move the pivoted member 41 off theabutment 49, the bimetal element 64 being energized for movement by anelectric heating coil 95. The bimetal element 64 is also engageable witha flexible" stop member 61 which is'operable after heating and movementof the bimetal element 94 to prevent the same from returning to itsinitial position upon cooling. 'A reset member 68 having movementsubstantially longitudinal of the stop member 61 has a portion 69operable upon movement to engage the stop member 61 to move or depressthe same to permit the bimetal element 64 to return to its initialposition. The reset member 68 also has a projecting portion 19 which isoperable upon movement to engage and move the panel 1.

pivoted member 41 off the abutment 46 and open switch 52. A conductor 1Iconnects the coil 28 of the relay switch 29 with the contact arm 34 fromwhich a conductor 12 runs to the fixed contact 54 of the switch 52. Aconductor 13 leads from the movable contact 53 of the switch 52 to theconnection point 14 on a conductor 15 completing a circuit to thesecondary I4 of the transformer I3. A resistor 19 connects theconnection point 25 on the panel 1 with a connection point 11 on theconductor 13. A resistor 13 and conductor 19 interconnect the fixedcontact 39 of the relay switch 29 and a connection point 89 on theconductor 13 and function to complete a holding circuit for the relayswitch 29 when the contacts 39 and 32 are closed. From the other fixedcontact 3I of the relay switch 29 a conductor 8I leads to a contactpoint 92 on the conductor II. A conductor 33 leads from the relaycontact arm 35 to the fixed contact 59 of the second relay switch 51.Another conductor 94 interconnects a connection point 85 on theconductor 83 and the contact arm 38 of the control switch 39. Aconductor 86 leads from the fixed contact 4| of the switch 39 to aconnection point 81 on the panel I, the circuit being completed byconductors 89 and 89 through the motor 3 to the ground conductor 5. Thepivoted arm 9! of the second relay switch 51 is connected by a conductor99 to the connection point 9! on the conductor 86. A conductor 92 runsfrom the fixed contact 49 of the switch 39 to a connection point 93 onthe panel I, the circuit being completed by conductors 94 and 95 throughthe primary 96 of an ignition coil 91 to the ground conductor 5. Aconductor 98 leads from a connection point 99 at the fixed contact 49 tothe heater coil 63 of the bimetal element 34 which is in turn connectedby a conductor I99 to a connection point IIlI on the ground conductor I0from the transformer I2. A conductor I92 leads from the coil 59 of therelay switch 51 to a connection point I93 on the Another conductor I94runs from the panel point I93 to the-fixed contact105 of a thermostaticstack switch I93. The thermostatic stack switch I95 has a movablecontact 191 ccoperable with contact I95, the movable contact I91 beingactuated by a thermostatic bimetal element I99 responsive to stacktemperature. The circuit through the stack switch I06 is completed by aconductor I99 running from the movable contact I91 to a connection pointI I9 on the conductor I1 to the thermostat I9. It should be noted thatin this form of the invention as illustrated in the drawing in Fig. 1the system is shown in its normal starting position prior toenergization.

In operation, this iorm of the invention functions as follows:

When electric current is supplied through the conductors 5, 6, I9 and II to the primary I2 of the transformer I3 the system is energizedsubjectto control of the various switches and control mechanismstherein. The initial circuit for the thermostat I9 runs from thetransformer secondary I4 through the conductors I5 and I1 to the fixedcontact of the thermostat. Assuming that when this system is initiallyenergized the space to be heated will be cold, the contact points I8 and20 of the thermostat I9 will be closed completing the circuit throughthe conductors 22 and 21 to the relay coil 28 and thence by conductors1| and 12 to the closed contacts 53 and 54 of the switch 52, returningby the conductors 13 and 15 to the transformer secondary I4. With thiscircuitclo'sed through'the thermostat I9, the coil 28 of the relay 29 isenergized and will cause the contacts 32 and 33to close against thefixed contacts' 39 and 3|. The closing of the contact 32 against thecontact 30 completes a circuit from therelaycoil 28 through the closedcontacts 32,

and 30, the resistor 18, conductor 19 and conductors 13 and 15 to thetransformer secondary I4. This last-named circuit is a holding circuitfor the relay switch 29 and will hold the same closed so long as thetransformer I3 remains energized and-the thermostat remains closed. Theresistor 18 functions as a drop out resistor so that if the voltagesupplied to the coil 28 should drop below a predetermined minimum valuethe voltage drop through the resistor 18 would be so great that therewould not be sufiicien't current through the coil 28 to hold the switch29closed. The conductor' 8I leads from the connection point 82 onthe-hot conductor II to the contact 3| of the relay switch 29 and whenthe relay switch 29 is closed a circuit is completed through the contactarm-35 and the conductors 83 and 84 to the control switch 39. Thecontrol switch 39 functionsto control the energizationof the circuitsthrough the motor 3 and the ignition coil 96 respectively by control ofthe contact points 43 and 42 respectively. It is seen then that when thesystem is initially energized the thermostat I9 closescausing'therelay'switch 29 to close establishing a holding circuittherethrough and energizing a circuit through the'motor 3 through theswitch contacts 4| and 43 and the conductors 86, 8'8 and 89, and a,circuit through the ignition coil through the contacts 42 and 40 andconductors 92, 94 and 95. At the same time that the circuit through theignition coil 96 is energized a branch circuit is completed through theconductor 98 to the heater coil 66 for the bimetal 64 and a conductorI98 leading to ground. If the system is functioning properly when themotor and ignition are energized there will be combustion and immediateoccurrence of flame in the burner I. The occurrence of flame in theburner I will cause the thermostatic switch I96 to be heated therebyclosing the contacts I05 and I01 and completing a circuit from thetransformer secondary I4 through the conductors I5, I1, I99, I04, andI92 to the coil 58 of the second relay switch 51, which circuit iscompleted back to the transformer secondary by the conductor 15. Theenergization of the last-named circuit through therelay coil 58 willcause the switch contact 69 to close and by movement of the contact armBI and'abutment 63 'willmove the pivoted member 41 clear of the abutment46 thereby permitting the switch 39 to open, because the contact arm 35of the relay switch 29 in closing moved free of engagement with thecontact arm 38 of the switch 39 thus leaving the pivoted member 41 inprimary control of the switch 39. The opening of the switch 39, byopening the contacts 42 and 43, causes the circuit through the motor 3and the ignition coil 96 to be. de-energized, but the closing of thecontacts 69 and 59 of'the second relay switch 51 establishessubstantially simultaneously a second motor circuit (this second motorcircuit running by conductor 8| to the closed contacts 3I and 33 of therelay switch 29, by the contact arm 35, the conductor '83, closedcontacts 59 and 69 of the second relay switch 51, and the conductors 99,86, 8B and 89 through the motor 3 to the ground wire 5, this secondmotor circuit by-passing the open switch39). It shouldbe noted that themovement-or the pivoted member 41 which permits switch 39'to open alsoopens switch 52. However, the opening of switch 52 at this point ofoperation does not affect the operation of the relay coil 28 whichremains energized through the previously described holding circuit whichincludes relay switch contacts 30 and 32.

It is seen that in normal operation of this system the motor andignition are'initially energized but upon recognition of flame by thestack switch 196, the relay switch 51 closes causing the switch 39 toopen thereby de-energizing the motor and ignition circuits andenergizing a second motor circuit for the maintenance of fuel for theoperation of the burner.

If the contacts I and I01 of the stack switch 506 fail to close for anyreason (e. g., a failure of flame in the burner) or if the second relayswitch 51 should fail to function for any reason, the heating of thebimetal element 64 by the heating coil 66 will cause the abutment 65 toengage and move the pivoted member 41 off the abutment 46 and thuspermit the switch 39 toopen to de-energize the motor and ignitioncircuits, the switch 52 being opened simultaneously by movement of thepivoted member 41. This actionof the bimetal element 64 is a safetyfeature of this system to prevent the supplying of fuel to the burner Iif there is a failure of ignition in the burner or a failure of theflame recognition circuit. When the bimetal element 64 moves to itssafety operated position it moves past the end of the flexible stopmember 61 which slips into position behind the bimetal element 64thereby preventing the same from returning to its initial position uponcooling. This last-named safety action causes the pivoted member 41 tohold open the switch 52 and thus functions to prevent immediatere-energization of the circuit by opening and subsequently closing thethermostat I9 until investigation has been made to attempt to determinewhy there has been a failure of the system to function. (Without thislast-named safety feature, if the flame recognition circuit failed tofunction for any reason and the system was moved to safety position asheretofore described, the circuit could be re-established by opening andclosin of the thermostat I9 whereupon the system would again begin itscycle of operation as heretofore described, continued cycling of fuel inthis manner without ignition thereof would cause a dangerous flooding ofthe burner.) To reestablish the system after safety operation of thebimetal element 64, the thermostat I9 should be opened to tie-energizethe holding circuit through the coil 28 of the relay switch 29 to permitthe same to ope This opening of the relay switch 29 will cause the pivotarm portion 31 to engage the contact arm 38' and close the controlswitch 39.

The reset member 93 should then be pushed in so that'thearm 69 willengage the flexible stop member 61 to move the same downward to permitthe bimetalelement 64 to return to its initial position andupon releaseof the reset member 69 the pivoted member 41 can return to its initialposition, The arm 10 permitting the switch 52 to close. of the resetmember 68 is operable upon movement to engage and move the pivotedmember 41, this last-named action being an additional safety feature ofthe system so that the reset member 68 may not be held in actuatedposition so that the re-starting of the system after safety operationcan be controlled from the thermostat alone. If the arm 19 was notemployed and the reset member 68 were permanently in actuatedposition,-the flexiblestop member -61 would-never function and thebimetal element 64 would always return to its initial position uponcooling and the system could be re-started by opening and closing of thethermostat I9. The arm of the reset member 66 by its engagement andmovement of the pivoted member 41. is operable to hold open the switch52 and thus break the initial circuit for the relay coil 29 of the firstrelay switch 29.

In the form of the invention illustrated in Fig.

'2 there is a burner III having an air and fuel supply means I I2 drivenby an electric motor H3 and having an electric spark ignition 5 I4.There is a main electric power source H5 leading to a main line switchII6 from which conductors H1 and H8 lead to connection points I I9 and Irespectively on a connection panel I2I. As in the previous form-of theinvention described the various electric circuits are shown connectedthrough the connection panel I2I and in commercial construction theconnection panel and all elements of the system to the right thereof onthe drawing would be enclosed in a casing or housing as a control devicefor the system.

From the control panel I2I two conductors I22 and I23 lead to theprimary I24 of a transformer I25. There are three secondary portions,I26, I21 and I28, for the transformer I25 from which run the variouscontrolling circuits for the system. There is a thermostat I29 which'isresponsive to the heat output of the burner III and is operable tocontrol energization of the system. The thermostat I29 has a fixedcontact I30 and a movable contact I'3I which is carried by a bimetalelement I32. The thermostat I29 has a compensating resistor I33connected in a shunt circuit from the bimetal element I32 which isoperable to reduce hunting by the thermostat I29. There is a relayswitch I34 having a coil I35 which is controlled by the thermostat I29for controlling the system. The relay switch I34 has three pairs ofcontacts carried by two contactcarrying arms I56 and I31 and is held bya spring I39 so that two pairs of its contacts I39, I40 and MI, I42 areinitially open and one pair of its contacts I43 and I44 are initiallyclosed. An end portion I45 of the contact arm I36 having an insulatingabutment engages and holds closed the contact arm I46 of a controlswitch I41 which is urged towards open position by a spring I48 and hasits opening movement limited by a stop member I49. The contact arm I46has a nonmetallic abutment portion I50 thereon against which ispositioned a pivoted member I5I which is operable to control theoperation of the switch I41 after the contact arm portion I45 of therelay switch I34 has moved away from engagement with the contact armI46. The pivoted member I5I is urged towards its position of engagementwith the abutment I56 by a spring I52 and is limited in its direction ofmovement by a stop member I53. The upper portion I54 of the pivotedmember I5I is operable upon movement to engage and move the contactcarrying arm I55 of a single pole double throw type switch I56 which hasone pair of contacts I51 and I59 initially closed, and a second pair ofcontacts I59 and I60 initially open. The contact-carrying arm I55 of theswitch I56 has positioned thereon a magnetic armature I6I which iscooperable with a permanent magnet I62 adjacent the contact I58 andwhich is operable to cause the switch I56 to move with a snap action.The contactcarrying arm I55 is of a cantilever construction, the contactI51 and I58 being urged by the spring 'force of the arm I55 towards aninitially closed position. There is a second relay switch I63 having acoil I64 and a fixed contact I65 and movable contact I66. The movablecontact I66 is carried by the pivoted contact-carrrying arm I61 and isurged towards open position by a spring I68. The contact-carrying armI61 of the relay switch I63 has an insulating material abutment portionI69 thereon which is cooperable with the pivoted member I5I to causemovement thereof upon closing movement of the relay switch I63. Abimetal element I10 having an insulating material abutment portion HIand heating coil I12 therefor is cooperable with the pivoted member I5Iupon heating and is operable to cause movement thereof. An electron tubeI13 is connected in circuit with the relay switch I63 and is operable tocontrol the same. The electron tube I13 is of a type having a controlgrid I14 which is controlled by a photo-electric cell I15 in circuittherewith. From the secondary portion I26 of the transformer I25 thereis a conductor I16 leading to a reset switch I11 which is held by aspring I18 in a normally closed position. A conductor I19 leads from thereset switch I11 to a connection point I on the panel I2I from whichanother conductor I6I leads to the fixed contact I30 of the thermostatI29. A conductor I82 connects the bimetal element I32 of the thermostatI29 with the connection point I83 on the panel I2I which is connected bya conductor I84 to the coil I35 of the relay switch I34. The coil I35 ofthe relay I34 is connected toa conductor I85 which interconnects thefixed contact I42 of the relay switch I34 and the fixed contact I58 ofthe switch I56, there being a resistor I86 in series with the conductorI81 runs from the contact arm I55 of with the coil I35 and the fixedcontact I42. The conductor I81 runs from the contact arm I55 of theswitch I56 to a connection point I88 on a conductor I89 whichinterconnects the contact arm I31 of the relay switch I34 and theconnection point I90 on the secondary portion I26 of the transformerI25. The compensating resistor I33 on the thermostat I29 is connected bya conductor I91 to aconnection point I92 on the panel I2I which is inturn connected by a resistor I93 to a connection point I94 on theconductor I81. The electron tube I13 has a cathode I95 which is heatedby a cathode heater element I96. The cathode heater element I96 isenergized by a circuit from the secondary portion I21 of the transeformer I25 through conductors I91, I98 and I99. The secondary portionsI21 and I28 are connected at'a connection point 200 to which isconnected the conductor I98. From a connection point 20I on theconductor I98 a conductor 202 connects with the connection point I90 onthe secondary portion I26 thus providing an operative interconnection ofthe three transformer secondary portions. The electron tube I13 has ashield grid 203 which is connected by conductors 204 and 205 and by aresistor 206 and capacitance 201 to ground at 206. The cathode heatercoil I96 is connected to the shield grid 203 by conductors I99, 299, 205and 204. The control grid I14 of the electron tube is connected byconductor 2I0 and a resistor 2 to the cathode 2I2 of the photo-electriccell I15. The photo-electric cell I15 has an anode 2I3 which isconnected to ground at 2I4 by a conductor 2I5. The photoelectric cellI15 is housed in and surrounded by a casing or shield I15 which admitslight only from the burner flame so that the cell I15 is solelyresponsive thereto. The conductor 2I0 which connects the photo-electriccell I to the control grid I14 has a shield 2I6 therearround to preventcapacitance between the conductor 2H] and the system. The conductor 2I1connects the shield 2I6 to ground to prevent capacitance between theshield 2I6 and the system. A capacitance 2I6 is positioned between theconductor 2I0 and the secondary portion I26 so that the current on thecontrol grid I14'will be out of phase with the current on the plate oranode 2 I9 of the electron tube I14 to such an extent that a very slightchange of current upon the control grid I14 will render the electrontube I13 conductive, the capacitance 2I8 also functions to determine thecharge or negative bias on the control grid I14. There is a resistor 220and conductor 22I runnin from the anode 2I9 of the electron tube I 13 tothe coil I64 of the relay switch I63 and another conductor 222 leadingfrom the coil I64 to the secondary portion I28 of the transformer I25. Acapacitance 223 is positioned between connection point 224 on theconductor 222 and the conductor 22!. Another capacitance 225 ispositioned between the conduc tor 264 and the conductor 22I.The'capacitors and resistors positioned in the circuit around theelectron tube function to reduce capacitance within the tube and toprevent radio interference. A conductor 225 runs from the cathode I95 ofthe electron tube I13 to the contact I44 of the relay switch I34 fromwhence another conductor 226 runs to the fixed contact I60 of the switchI56. A conductor 221 runs from the hot conductor I23 to the fixedcontact I 43 of the relay switch I34. The contact arm I36 of the relayswitch I34 is connected by a conductor 221 to the fixed contact I55 ofthe relay switch I63 and is connected at a connection point 228 to thecontact arm I46 of the control switch I41. The control switch I 41 hastwo fixed contacts 229 and 230 and two movable contacts 23I and 232respectively cooperable therewith which are carried by the contact armI46. A conductor 233 runs from the fixed contact 229 of the switch I41to a conductor 234 which connects through a connection point 235 on theconnection panel I 2I to the primary coil 236 of the ignitiontransformer 231 and thence by a conductor 238 to the ground conductorII1. From the junction point 239 of the conductors 233 and 234 aconductors24ii runs to the heater coil I12 for the bimetal element I10,another conductor 24I completing'the circuit from the heater coil I12 tothe ground conductor I32. From the fixed contact 233 of the switch 541 aconductor 242 connectswith aconductor 243 leading to the connectionpoint 26-4 on the connection panel I2I from whence a conductor 245 leadsto the motor II 3 and a conductor 249 completes the circuit to, theground conductor II'i'. From the junction point 241 of the conductors242 and 243 a conductor 243 connects with the contact arm I61 of therelay switch I 53.

In this system the position and operative relationship of parts are asshown in Fig. 2 before the system is energized. When the main switch II6is closed. the circuit through the conductors II 1, I I8, I22 and I23 iscompleted through the transformer primary I24 thus preparing the systemfor operation. With the transformer I25 energized, a circuit isenergized for the heater coil I 96 of the. electron tube I13 and thetube I13 begins to heat in preparation for controlling the system. Whenthe thermostat I29 closes calling for heat, a circuit is 'ompletedfromthe 10 transformer secondary portion I26 through the conductor I 16, thereset switch I11, the conductors I19 and I8I, the closed contacts I30and I3I of the theromstat I29, the conductors I82 and I84, the relaycoil I35, the conductor I85, the closed contacts I51 and I 58 of theswitch I56, the conductor I81, and the conductor I89 leading to thetransformer secondary portion I26 at the connection point I90. Thislast-named circuit energizes the coil I35 of the relay switch I34causing the contacts I39 and MI to close against the fixed contacts I40and I42 respectively and the contacts I43 and I44 to open. When thecontacts MI and I42 of the relay switch I34 are closed, the circuitthrough the coil I35 is then completed through the resistor I86 and theclosed contacts I 4!, I42 to the conductor I89 leading to thetransformer secondary portion.I26. This last-named circuit is a holdingcircuit for the relay coil I35 which will be energized at all times thatthe main switch Iii-3 is closed and the thermostat I23 is closed. Beforethe relay switch I34 closes there is a circuit running from the cathodeI of the electron tube I13 through the conductor 225 the closed contactsI43 and I44 of the relay switch I34, the conductors I89 and 202, thesecondary portion I28, the conductor 222, the relay coil I 64, theconductor 22I and the resistor 220, the circuit being completed to theanode 2I9 of the electron tube I13. This lastnamed circuit is operativeas a safety means, the operation of which will be described at a latertime. With the contacts I39 and I40 of the relay switch I34 closed,there is a circuit established from the hot conductor I23 through theconductor 226, the closed contacts I39 and I40 and the contact arm I36,and the conductor 221 to the contact arm I46 of the control switch I41.At the control switch I41 the aforementioned circuit divides and aportion of the same is completed through the conductors 242, 243 and 245to the motor II3, the circuit being completed to the ground conductor II1 by conductor 246. This last-named circuit functions to energize themotor II 3. Another portion of the circuit from the switch I41 runs fromthe contacts 229 and 23I through a conductor 233 to the connection point239 where the circuit divides, a portion of the circuit being completedthrough conductors 234 and 236 through the ignition coil 236 to theground conductor II1, and another portion of the circuit runs throughthe conductor 240 to the heater coil I12 for the bimetal element I10 andis completed through the conductor 24I to the ground conductor I22.These last-mentioned circuits energize the ignition elec trodes H4 forthe burner III and the heater coil I12 for the bimetal element I10respectively. When the relay switch I34 is closed and the contacts I43and I 44 are open the aforementioned circuit from the cathode I95 of theelectron tube I13 through the coil I64 of the relay switch I63 isbroken. As the heater coil I12 heats the bimetal element I10 thiselement moves the abutment I1I against the pivoted member I5I causingthe same to move. After a predetermined period of heating by the heatercoil I12 the bimetal element I10 will cause the abutment I1I to move thepivoted member I5! until the upper portion I54 engages and moves thecontact arm I 55 of the switch I 56. Thismovement of the pivoted memberI5I will cause the contact arm fuel to be ignited at the burner thesystem functions normally, the fuel is ignited 11 pivoted member I irequired to close the contact I59 and I60 of the switch I66 is sodetermined that the pivoted member I5I will not have moved clear of theabutment I50 of the switch I41 at this time. This position of movementof the bimetal element I10, the pivoted member I5I and the contact armI55 is illustrated in Fig. 3 wherein the bimetal element I has moved theaforementioned parts to the position described thus closing the contactsI59 and I60 and thereby establishing a second circuit from the cathodeof the electron tube I13. This second cathode circuit is operativethrough the conductors 225 and-.226, the closed contacts I59 and I60 ofthe switch I56, the conductors I81, I89 and 202, the secondary portionI28, the conductor 222, the relay coil I64, the conductor 22I and theresistor 220, the circuit terminating at the anode 2 I9.

At this point in the operation of the system, with the thermostat I29closed and the circuits to the ignition and to the motor through theswitch I41 energized, the closing of the contacts I59 and I60 of theswitch I56 establishes a second cathode circuit rendering the systemresponsive to the occurrence of flame at the burner III. With the motorand ignition circuits energized, the next step in the normal sequence ofoperation of the system would be for the III. If

at the burner III and the occurrence of flame will cause thephoto-electric cell I to become energized and drain a negative potentialfrom the control grid I14 of the electron tube I13 thus rendering theelectron tube I13 conductive. When the electron tube I13 is thusrendered conductive by the occurrence of flame at the burner III currentwill be able to flow through the electron tube thus completing thesecond cathode circuit and energizing the relay coil I64.

' Fig; 4. When the switch I41 is opened by the aforementioned movementof the pivoted member I5I the opening of the switch contacts 229 and23I, 230 and 232 will de-energize the circuits to the motor II3, theignition transformer 236, and the heater coil I12, these elements havingbeen described heretofore as being in circuit with the switch I41. Theclosing of the relay switch I63 simultaneously with the opening of theswitch I41 causes the establishment of a second circuit for the motorfrom the hot conductor I23 through the conductor 226, the closedcontacts I39 and I40, the contact arm I36, the conductor 221 the closedcontacts I65 and I66 of the relay switch I63, the contact arm I61, theconductor 248, and the conductors 243, 245 and 246 through the motor II3to the ground conductor II1.

It is seen then that in normal operation when the system is energizedand the thermostat I29 calls for heat, the relay switch I34 closesestablishing a holding circuit for itself and energizes circuits for themotor II3, the ignition H4 and the heater coil I12 through the switchI41. The heater coil I12 then functions as a timer for moving thecontact arm I5I to close the switch contacts I59 and I60 to establish asecond circuit from the cathode, the length of time for this 12operation being substantially that required for the heating of theelectron tube I13. The occurrence of flame then at the burner III causesthe activation of the electron tube I13 and completes the circuitthrough the relay switch I63 causing the same to close and thusde-energizing the motor, ignition, and heater coil circuits andsubstantially simultaneously energizing a second motor circuit. If, forany reason, the relay switch I63 fails to close at the time when theheater coil I12 and the bimetal element I10 have moved the pivotedmember I5I and contact arm I55 to establish the aforementioned secondcircuit from the cathode, the heater element I12 will continue to causethe bimetal element I10 to move the pivoted member I5I. If the relayswitch I63 then fails to close before the pivoted member I5I moves clearof the abutment I50 the switch I41 will be opened thus deenergizing themotor, ignition, and heater coil circuits. This last-mentioned operationis as shown in Fig. 5 and functions as a safety for the system in theevent that the relay switch I63 fails to close. (The failure of flame atthe burner III or the failure of the electron tube I13 to function arethe principal causes of such safety operation but the safety operationwould function as described should the relay switch I63 fail to closefor any reason whatsoever.) When the bimetal element I10 has cooled andreturned to its initial position after'the safety operation, the pivotedmember I5I will not be able to return to its initial position because ofits engagement with the edge of the abutment I50 of the switch I41.After such safety operation the system will not be able to functionagain until the relay switch I34 is permitted to open (the relay switchI34 being held closed by its holding circuit during safety operation).If the circuit through the coil I35 of the relay switch I34 is opened,either by opening the thermostat I29 or by opening the reset switch I11,the holding circuit for the coil I35 will be broken thus permitting thespring I38 to move the switch I34 to its initial open position. Thisopening movement of the relay switch I34 will cause the end portion I45of the contact arm I36 to engage the contact arm I46 of the switch I41causing the same to be closed since the spring I38 is stronger than thespring I48. Upon this closing of the switch I41 by the relay switch I34the spring I52 will then be able to move the pivoted member I5I backinto engagement with the abutment I50. This last sequence of operationplaces the system in its initial operating condition and renders thesame operative upon closing of the thermostat I29 and the operation ofthe other units of the sys tem as heretofore described. If, while thesystem is energized and in its initial or off position, as shown in Fig.2, the conductor 2I0 from the control grid I14 should become shortedgiving a continuous and false indication of flame at the burner III, thefirst-named circuit from the cathode I through the closed contacts I43and I44 of the relay switch I34 will function as a safety means toprotect the system. If the described condition occurs, the electron tubeI13 will become conductive permitting a completed circuit through therelay coil I64 and causing the relay switch I63 to close. The closing ofthe relay switch I63 will cause the pivoted member I5I to be moved, aspreviously described, thus opening the switch I41 and the switchcontacts I51 and I58 of the switch I56. The opening of the switch I 41will protect the system in that "as a. unit control device. "twoconductors 258 and 251 lead to connection points 258 and 258respectively. From the conheat output of the burner 249.

with a fixed contact 29!.

Inthe system shown in Fig. 6 there is a modifi cation of the form shownand described in Fig. 2 with certain safety features added andmodification of the circuits for the adaptation of these safetyfeatures.

"There is a burner 249 having a fuel and air supply'blower 258 driven bya motor 25! and having an electric spark ignition 252.

Electric power for the system is supplied from a main power source 253and is controlled by a switch 254. As was described in the previousforms of "this invention the circuits are shown as beingconnectedithrough a connection panel 255 and in commercial constructionall of the elements :shown to the right of the connection panel wouldbe. assembled within a casing or other enclosure From the switch 254nection points 258 and 259 the circuit is con pleted' through theprimary 288 of a transformer 28! by. conductors 282 and 283. Thetransformer 26! has three secondary portions 264, 285 and 266'from whichrun the circuitsfor the energization of the system. A thermostat 281 isconnected i 268, 269 and 218 and is operable to control the operation ofthe system by its response to the The thermostat 251 has a fixed contact21! and a movable contact 212 carried by a bimetal element 213 fromwhich is connected a resistor 214 which is operable to compensate thethermostat for irregular variations in temperature. The contacts 21! and212 and the compensating resistor 214 are con- The thermostat 261 isenergized by a circuit running from the "secondary portion 284 of thetransformer 28! which is connected by a conductor 218 to a connectionpoint 218 on the connection panel 255. From the connection point 288 onthe connection panel 255 a conductor 219 runs to a relay coil 288 of arelay switch 28!. The relay switch 28! has two pivoted contact-carryingarms 282 and 283 which carry the movable contacts 284, 285 and 288, thecontacts 284 and 285 being carried by the contact arm 282. The contacts288 and 285' are engageable'with the fixed contacts 231 and'288respectively, which are carried by flexible supporting members 289 and298. The contact 288 carried by the'contact arm 283 is engageable Theswitch contacts 281 and 284 are initially closed and the contacts 285,288, 286 and 29! are initially open, the switch'being held in thisinitial position by a spring 292. The flexible contact arm 289 isinherently flexed towards a stop member 293 towards which it will moveupon closing movement of the switch 28!. The flexible contact arm 288 islikewise tensioned against the stop member 294. When the relay switch28! is closed, the contact-carrying arms 282 and 283 move downward underthe attraction of the relay coil 288 member 293 is so positioned thatthe contact 288 will" not "break away from the contact 281 until contacthas been made between the'contacts 285 and 288'which movement continuesuntil the. contacts 288 and 29! are closed andthe flexible contact arm298 is tensioned away from the stop member 294. Upon opening movement.of the relay switch 28! a similar action takes place in that the contact288 will not break from thecontact 29! until contact has been madebetween the contacts 284 and 281. The pivoted contact-carrying arm 282of the relay switch 28! has an electrically insulated end portion 295which is engageable with the contact carrying arm 2980f a switch 291when the relay switch 28! is in its initial open position. Thecontact-carrying arm 298 is urged by a spring 298 towards an openposition but is limited in this movement by a stop member 288.. Thecontact arm 296 carries two contacts 388 and 38! thereon which. areengageable with fixed contacts 382 and 383 respectively. The contact arm299 has a non-metallic abutment member 384 thereon which is engageableby a pivoted member 385 which ls'operable to hold the switch 291 closedwhen the pivoted arm portion 295 of the relay switch 29! is not inengagement therewith. The pivoted member 385 is held in its position ofengagement with the abutment member 385 by a spring 386 and is limitedin this direction of movement by a stop member 381. The upper portion388 of the pivoted member 385 is engageable with the contact carryingarm 389 of a switch 3!8. The switch 3!8 has a fixed contact 3!! and amovable con tact 3!2 carried by the contact arm 389, the contact arm 389being ofa cantilever construction and urging the contacts 3! and 3!2towards engagement, The contact arm 389 carries a magnetic armature 3!3which is cooperable with a permanent magnet 3M adjacent the fixedcontact 3i! and is operable to cause the switch 3!!! to open and toclose with a snap action; A second relay switch 3i5 has two pivotedcontact carrying arms 3l5 and 3!1, the pivoted contact arm 3!1 having anelectrically insulated abutment portion 3!8 thereon which is operableupon movement to engage and move the pivoted memher 385. The relayswitch 3!5 has a coil 3!!! which is operable on energization to move thecontact arms 358 and 3! 1, the same being held in an open position by aspring 328. The relay switch 3!?! has two movable contacts 32! and 322which are carried by the pivoted contact arms 3!5 and 3H respectively,and two fixed contacts 323 and 828 which are carried by two flexiblesupporting members 325 and 328. The relay switch 3!5 is operable uponclosing movement to cause the abutment member 3! 8 to engage'and movethe pivoted member 385 clear of the abutment 384 thus permitting theswitch 291 to open and simultaneously by engagement of the upper portion388 with the contact arm 389 to cause the switch'3l8 to open. The fixedcontacts 323 and 324 of the relay switch 3l5 are so positioned inrelation to the movable contacts 32! and 322 that when the relay switch3!5 closes the contacts 322 and 324 will engage prior to the opening ofthe switch 3!!) and the relay switch M5 and will have an overtravelmovement due to the flexibility of the flexible contact arms 325 bimetalelement 321 has a flexible stop member 339 engageable therewith which isoperable to prevent the same from returning to its initial position uponcooling after having performed its safety function. A reset member 33!has an arm portion 332 engageable with the flexible stop member 339 uponmovement and is operable to move the same to permit the bimetal element321 to return to its initial position upon cooling. The reset member 33!also has an arm portion 333 which is operable upon movement to engageand move the pivoted member 395 to open the switch 3!!) and to hold thesame open so long as the reset member 33! is in its operated position.The reset member 33! also has a side arm or projecting portion 334 whichis engageable upon movement with the operating arm 335 of a reset switch333 and is operable to open and to hold open the same while .in operatedposition. In circuit between the switch 3H} and the relay switch 28! isan electric timing switch 331 which operates to delay the functioning ofthe relay switch 28! for a predetermined time. The timing switch 331 hasa fixed contact 333 and a movable contact 339, the movable contact 339being carried by a bimetal element 348. Through the switch 331 runs aresistor 34! which is operable to cause a sufiicient voltage droptherethrough to prevent operation of the relay switch 29! so long as theresistor 34! is functioning. The bimetal element 349 of the timingswitch 331 is responsive to the heat generated by the resistor 34! andis operable after a predetermined period of heating to warp so that thecontacts 338 and 339 will close and establish a shunt circuit throughthe bimetal element 349 which has a very low resistance compared to theresistor 34!. The relay switch 3!5 has an electron tube 342 in circuittherewith, said electron tube being operable to control energization ofthe relay coil 313. The electron tube 342 is of the controllable gridtype having a control grid 343 which is controlled by a. photo-electriccell 344 which is responsive to the occurrence of flame at the burner249. From the relay coil 28!] of the relay switch 28! there is aconductor 345 leading to the reset switch 338 which is in turn connectedby a conductor 346 to the pivoted contact arm 282 of the relay switch28!. From the flexible contact arm 289 of the relay switch 28! there isa conductor 341 leading to the timing switch 331 from whence a conductor349 leads to the contact arm 399 of the switch 3H3. From the fixedcontact 3!! of the switch 3|9 a conductor 349 runs to the contact arm 3Hof the relay switch 3 !5. From a connection point 359 on the conductor349 another conductor 35! leads to a connection point 352 on a conductor353 which together with a drop-out" resistor 354 interconnects theflexible contact arm 299 of the relay switch 28! and a conductor 355leading to the transformer secondary portion 264. The transformersecondary portions 265 and 256 are connected at connection point 356 andare together connected to the conductor 355 at a connection point 351 bywhich an operative interconnection of the three secondary portions isobtained. From the connection point 358 on the hot? conductor 252 aconductor 359 runs to the contact arm 283 of the relay switch 28!. Fromthe fixed contact 29! of the relay switch 28! a conductor 369 runs tothe contact arm 293 of the switch 291, a branch conductor 35! runningfrom a connection point 362 of the conductor 333 to the flexible contactarm 325 of the relay switch 3!5. From the fixed contact 393 of theswitch 291 the conductor 363 runs to the connection point 364 on theconnection panel 255, from whence a conductor 365 runs to the motor 25!which is in turn connected by conductor 366 to the ground conductor 251.From the fixed contact 392 a conductor 361 runs to the connection point368 on the connection panel 255 to which is connected-the primary 369 ofthe ignition transformer 319 which is in turn connected to the groundconductor 251 by a conductor 31!. A branch conductor 312 runs from theconnection point 313 on the conductor 361 to the heater coil 328 of thebimetal element 321 from whence a conductor 314 runs to the groundconductor 263. The electron tube 342 has a cathode 315 which is heatedby a cathode heater coil 316. The electron tube 342 has a screen grid311 and an anode 918. The cathode heater coil 316 is connected by aconductor 319 to thetransformer secondary portion 265 and is connectedto the conductor 355 at a connection point 399, the circuit from theconductor-355 being completed back to the transformer secondary portion255 by a conductor 38! interconnecting the connection points 356 and 351thus completing the cathode heater circuit. The circuit from thecompensating resistor of the thermostat 251 is completed from theconnection panel at point 299 by a conductor 382 having a resistor 383therein to a connection point 384 on the conductor 355. From the cathode315 of the electron tube 342 a conductor 385 runs to the flexiblecontact supporting member 326 of the relay switch 32' 5. A conductor 386runs from a connection point 381 on the conductor 395 to the contact arm399 of the switch 3H3. From the transformer secondary portion 266 aconductor 388 runs to a connection point 389 from whence anotherconductor 39!] runs to the coil 3!9 of the relay switch 3!5. From thecoil 3!9 of the relay switch 3l5 the conductor 39! runs to a connectionpoint 392 from whence a resistor 393 completes the connection to theanode 318 of the electron tube 342. A capacitance 394 is positionedbetween the connection point 395 on the conductor 39! and the connectionpoint 389 at the juncture of the conductors 388 and 396. At theconnection point 392 a capacitance 396 is connected which is in turnconnected by a conductor 39'! to a capacitance 398 at a point 399, thecapacitance 398 being grounded as at 469. A conductor 49! runs from theheater filament connection point 386 of the electron tube 342 to a point492 which joins a lead from the screen grid 311 and a conductor 483 fromthe connection point 399 of the capacitances 396 and 398, a resistor 494completing the connection from the point 492 to ground at 499. From thecontrol grid 343 of the electron tube 342 a conductor 495 having aresistor 496 therein leads to the cathode 401 of the photo-electric cell344. The conductor 405 and resistor 496 are shielded to preventcapacitance between the conductor 495 and the system. The photo-electriccell 344 has an anode 498 from whence a conductor 409 runs to ground asat 4H]; another conductor 4! runs from the shield M2 and joins theground conductor 499 at a connection point 4!3. There is a conductor 4H4running from the connection point M5 on the conductor 495 to acapacitance H6 which is connected to the transformer secondary portion234 at a connection point 4 1.

The operative relationship of the various parts of the system as isshown in Fig. 6 corresponds to the initial condition of the system priorto energization. When the main power switch 254 17 is closed thetransformer 261 is energized and the system is ready to function subjectto the various controls therein. The electron tube cathode heater coil316 is energized by the transformer secondary portion 265 as soon ascurrent is supplied to the transformer primary 260 and the electron tube342 then begins to heat in preparation for its functioning later on.When the thermostat 261 closes calling for heat a circuit is completedfrom the transformer secondary portion 254 through the conductors 218and 215, 4'

the closed contacts 211 and 212 of the thermostat 261, and theconductors 216 and 219 to the relay coil 280. From the relay coil 280the ,cirr cuit continues through the conductor 345, the reset switch336, the conductor 346, the closed contacts 284 and 281, the conductor341, the resistor 341 of the timer switch 331, the couductor 348, theclosed contacts 311 and 312 of the switch 310, the conductors 351 and353, and the conductor 355 terminating back at the transformer secondaryportion 264. This last-named circuit as described is completed throughthe relay coil 230 but the voltage drop through the resistor 341 is sogreat that there is not sufficient current through the relay coil 280 tocause the relay switch 231 to close. While this great voltage drop istaking place through the resistor 341, the same is heating andtransmitting heat to the bimetal element 340 so that after a predeter-F,

mined time the bimetal element 340 will warp to such an extent that thecontacts 338 and 339 of the timer switch 331 will close thusestablishing a shunt circuit of lower resistance through the bimetalelement 340 so that the relay coil 283 is able to function and close therelay switch 281. When the relay switch 281 closes, the contacts 284 and281 are broken apart and the contacts 285, 288, 286 and 291 respectivelyare closed. The closing of the contacts 285 and 288 establish a holdingcircuit for the relay coil 280 which is completed through the closedcontacts 285 and 288, the resistor 354 and the conductors 353 and 355terminating at the transformer secondary portion 264. The resistor 354which is connected in series with the relay coil 280 in the holdingcircuit for the relay switch 281 is of a suflicient re: sistance tocause a voltage drop therethrough which will render the relay coil 2 80inoperative or cause the relay switch 281 to open should the v voltagein the circuit drop below a predetermined minimiun value. The closing ofthe holding circuit for the relay coil 280 and the opening of thecontacts 284 and 281 cause the circuit through the timer switch 331 tobe broken and the holding circuit to be independent of the circuitthrough the timer switch 331. At the time the system is first energizedand prior to the closing of the thermostat 261 and the relay switch 261there is a circuit established from the cathode 315 of the electron tube342 through the conductors 385 and 386, the closed contacts 311 and 312of the switch 310, the conductors 351, 353, 355 and 381, the transformersecondary portion 266, the conductors 3.88 and 390 to the relay coil 319of the relay switch 315, the circuit being completed by the conductors391 and resistor 393 leading back to the anode 318 of the electron tube342. Since this circuit operates through the closed contacts of .theswitch 310 and (as will be explained later) since the switch 310 will beopened upon activation of the electron tube 342, this circuit functionsas a fsafety for the system in the event that the control grid of theelectron tube 3.42 should become shor ed 18 giving a false indication offlame while the system is in an off position. When the contacts 286 and291 of the relay switch 281 are closed a circuit is completed from thehot conductor 262 through the conductor 359, the closed contacts 286 and291 and the conductor 360 to the switch 291. Through the closed contacts301 and 303 of the switch 291 a circuit is completed through the motor251 by the conductors 363, 355 and 366. Through the closed contacts 300and 302 of the switch 291 the circuit is completed through the ignitioncoil primary 369 by the conductors 361 and 311, a branch circuit runningfrom connection point 313 on conductor 361 over the conductors 312 and314 through the heater coil 328 of the bimetal element 321. It is seenthen that upon energization of the system the primary of the transformer261 is energized thus energizing a circuit for the heater coil 316 ofthe electron tube 342. When the thermostat 261 closes the circuit iscompleted through the coil 280 of the relay switch 281, but due to thevoltage drop through the timer switch 331 the relay switch 281 is notable to function. After a predetermined time the timer switch 331establishing a shunt circuit around the high resistor therein permittingthe relay switch 281 to close, the aforementioned predetermined time foroperation of the timer switch 331 being at least that required for theheating of the electron tube 342. When the relay switch 281 is closed aholding circuit is established for the relay coil 280 and circuits areenergized through the control switch 231 to the motor, the ignition andthe heater element of the bimetal element 321. At this point in theoperation the system is ready to function subject to the occurrence offlame at the burner 249. If upon the aforementioned energization of thecircuits through the motor and the ignition, the system should functionnormally and flame occur in the burner 249 the photo-electric cell 344will function to drain a negative potential from the control grid 343 ofthe electron tube 342 thus permitting the passage of electric currenttherethrough. The photo-electric cell 344 is housed in a casing 344 toshield it from response to extraneous light rays not emitted from theburner flame. Upon the electron tube 342 becoming conductive theaforementioned circuit from the cathode of the electron tube through thecoil 319 of the relay switch 315 is completed and the relay switch 31 5will close. The closing of the relay switch 315 will cause the contactarm 31! to move the abutment member 318 against the pivoted member 305moving the same free of the abutment 304 permitting the switch 291 toopen and simultaneously engage the contact arm 309 of the switch 310with the Upper portion 308 of the pivoted member 305 causing the switch310 to open. As was described heretofore the fixed contacts 323 and 324of the relay switch 315 are mounted upon flexible supporting members 325and 326 so that the movable contacts 321 and 322 upon closing movementmay contact the fixed contacts before the switch 310 is open. (This stepin the operation ofthe system is illustrated in Fig. 7. The contacts ofthe relay switch 315 are shown closed and the switch 310 has not yetopened.) The flexibility of the fixed contacts permits the movablecontacts of the relay switch 315 to have a predetermined amount ,ofovertravel during which overtravel the pivoted member 305 is moved.clear,of'the abutment 304 to permit the 19 switch 291 to open and theswitch 310 is opened by engagement of the upper portion 308 of thepivoted member 305 with the contact-carrying arm 309. This step of theoperation is shown in Fig. 8 in which the movable contact arms 316 and311 have moved past their point of engagement with the fixed contactsand the switches 291 and 310 are opened.) At this point, with the switch291 open and the relay switch 315 closed, a second circuit isestablished for the motor and a second circuit is established forholding closed the relay switch 315. The second motor circuit runs fromthe hot conductor 232 through the conductor 359, the closed contacts 286and 291 of the relay'switch 281, the conductors 330 and 361, the closedcontacts 321 and 323 of the relay switch 315, the conductors 383 and 363to the connection panel 255 and thence by conductors 365 and 366 throughthe motor 251 to the ground conductor 251. The second cathode circuitforholding the relay switch 315 closed runs from the cathode 315 of theelectron tube 342 by conductor 385 to the flexible contact arm 326 ofthe relay switch 3 I 5, through the closed contacts 322 and 324, theconductors 351, 353, 355 and 381, the transformer secondary portion 266,the conductors 388 and 3911 to the relay coil 319, the circuit beingcompleted by conductor 391 and resistor 393 to the anode 318 of theelectron tube 342. As was pointed out in the mechanical operation of therelay switch 315 against the pivoted member 305, these circuits throughthe contacts of the relay switch 315 are established before the switches291 or 310 are opened thus providing a continuous circuit independent ofthe opening of the switches 310 and 291. The opening of the switch 291de-energizes the first-named circuit to the motor 251, there-establishment of which has already been described, and the circuit to.the ignition transformer 310 and the heater coil 328 for the bimetalelement 321. It is seen then that in the normal sequence of operation ofthis system upon energization and upon calling for heat by thethermostat 261, the relay switch 281 is closed after a predetermineddelay caused by the time switch 331 to permit the electron tube 342 toheat, the closing of the relay switch 281 being operable to energize thecircuits to the motor 251, the ignition transformer 310, and the heatercoil 328 for the bimetal element 321. The occurrence of flame then atthe burner 249 will cause the electron tube 342 to become conductivethus completing the circuit through the relay switch 315 causing thesame to close thus opening the circuits for the motor, the ignition, theheater coil and the electron tube, a second circuit for the motor andfor the electron tube be.- ing established simultaneously with theopening of the aforementioned circuits. When the system is energized,the thermostat 281 is calling for heat and the relay switch 281 isclosed. If the relay switch 315 should fail to close for any reason (e.g. failure of flame at the burner, failure of the electron tube 342, ora break in the relay circuit) the heater coil 328 for the bimetalelement 321 will continue to heat, to operate as a safety means formoving the bimetal element 321 into engagement with the pivoted member305 to move the same clear of the abutment "304 to permit the switch 291to open and simultaneously to open the switch 310. At this point in thesafety operation the system is in substantially the same condition asthat shown in the form of the invention of Fig. 2 in that the switches291 and 310 are open and the relay switch 281 is closed by its holdingcircuit. The system at this point is in a lock-out position from whichposition the system cannot function until the switches 231 and 310 areclosed. In this form of the invention, however, there is a flexible stopmember 330 which is engageable with the bimetal element 321 uponoperation thereof to prevent the same from returning to its initialposition after safety operation so that the system may not be operatedagain after safety operation until a check has been made to determinethe cause of the failure. With the bimetal element 321 locked by thestop member 330 in its operated position the pivoted member 305 cannotreturn to its initial position and so even though the circuit throughthe thermostat 261 might be opened permitting the relay switch 281 toreturn to its initial position and closing the switch 291 by engagementof the pivoted contact arm portion 295 with the contact arm 295 thepivoted member 385 would still hold open the switch 310 thus preventingreenergization of the relay coil 280 until the bimetal element 32'! ispermitted to return to its initial position, When the reset member 331is pushed into engagement with the stop member 330, the stop member 330is moved clear of engagement with the bimetal element 321 and the sameis permitted to return to its initial position.

As an additional safety feature the reset arm portion 333 is engageablewith the pivoted member 3015 so that the reset member 331 may not belodged into operated position and the stop member 330 thereby renderedineffective. (If the reset member 331 should be held in operatedposition the reset arm portion 333 acting through the pivoted member 305will function to hold the switch 310 open thus preventing operation ofthe system.) -The projecting arm portion 334 of the reset member 331 iscooperable upon movement to engage the reset switch 336 to open the samesimultaneously with the resetting of the bimetal element 321 therebybreaking the circuit through the relay coil 280 independently of thethermostat 231. The described step in the sequence of operation of thesystem in which the bimetal element 321 has moved the pivoted member 305to safety position is clearly illustrated in Fig. 9. In operation if thefuel should fail to ignite in the burner 249 upon initial operation ofthe system the bimetal element 321 will move to safety position thuslocking the system as described until the reset member has beenoperated. If, upon initial operation, the fuel should ignite at theburner 249 and the system function normally as heretofore described, butduring the operation the flame, for some reason, should go out theelectron tube 342 would then be blocked for passage of currenttherethrough thus causing the relay switch 315 to open to de-energizethe motor circuit to prevent further supply of fuel to the burner 249.At this point in the operation since the bimetal element 321 has notmoved to safety position and the switches 291 and 310 are open thethermostat 261 must be opened or the reset member moved to open thereset switch to break the holding circuit through the relay coil 280 topermit the relay switch 231 to return to its initial position to closethe switch 291 and permit the pivoted member 305 to return to itsinitial position and the switch 310 to close. The relay switch 281 isable to close the switch 291 because the spring 282 is stronger than thespring 298. After the circuit has been opened through the thermostat 231and the relay switch 28! a subsequent closing of the contacts of thethermostat 261 will cause the system to function as though it were beingstarted initially, that is, the system will go through its normal cycleof operation and should the fuel fail to ignite at the burner 249 thebimetal element'32l will move to safety position as describedheretofore.

The systems as shown are applicable especially to the control of gun orrotary types" of liquid fuel burners having a blower and means forsupplying fuel in a fine spray to the burner. These systems, however,would also be adaptable to the control of pot type liquid fuel burnerswherein an electric blower supplies a forced draft of air to the burneror where the supply of fuel to the burner is controlled by an electricvalve such as a solenoid valve. It would also be possible to adapt thesecontrol systems to the burning of solid fuel in a finely divided statewherein a powdered fuel and air mixture would be supplied to the burnerby a blower which could be controlled by the system. It should thereforebe evident that although the systems have been described as specificallyapplicable to gun type oil burners, it is not intended that thisinvention shall be so limited.

Having thus described the invent-ion, what is claimed and is desired tobe secured by Letters Patent of the United States is:

1.111 a control device, a circuit including a switch, a relay switchoperable to control energization of said circuit, a second circuitincluding a third switch, said third switch being initially closed, apivoted member engaging and holding closed said first-named switch, saidpivoted member being operable upon predetermined movement to permit saidfirstmamed switch to open and to open said third switch, electric timingmeans operable after a predetermined time as safety means to move saidpivoted member through said predetermined movement, and means includinga second relay switch arm operable to engage said pivoted member and tomove the same to open said first-named and said third switches.

2. In a control device, a circuit including a switch, a relay switchoperable to control energization of said circuit, a second circuitincluding a third switch, said third switch being initially closed, apivoted member engaging and holding closed said first-named switch, saidpivoted member being operable upon predetermined movement to permit saidfirst-named switch to open and to open said third switch, a thirdcircuit connected in parallel with said first-named circuit, a secondrelay switch having contacts in said third circuit, said second relayswitch having a contact carrying pivoted member operable upon movementto close said contacts in said third circuit and also to engage and movesaid first-named pivoted member through said predetermined movementthereby to open said first-named and said third switches.

3. In a control device, a circuit including a switch, a relay switchoperable to control energization of said circuit, a second circuitincluding a third switch, said third switch being initially closed, apivoted member engaging and holding closed said first-named switch, saidpivoted member being operable upon predetermined movement topermit saidfirst-named switch to open and to open said third switch, a bimetalelement, an electric-heating coil for'said bimetal "element, saidbimetal element being operable upon heating for a predetermined time tomove said pivoted member through said predetermined movement thereby toopen said first-named and said third switches for safety operations, asecond relay switch having a pivoted member operable upon closingmovement to engage and move said first-named pivoted member through saidpredetermined movement thereby to open said firstnamed and said thirdswitches.

4. In a control device, afirst circuit and a second circuit, a switchhaving two pairs of contacts for controlling said circuits, a relayswitch having a pair of contacts in said first and said second circuitsand operable to control energization of said circuits, at third circuit,a second relay switch having a pair of contacts in and controlling saidthird circuit, said second relay switch being normally open, a fourthcircuit including a fourth switch, a pivoted memberengaging and holdingclosed said first-named switch, said pivoted member being operable upona predetermined movement to permit said first-named switch to open andto open said fourth switch, said second relay switch having a pivotedcontact-carrying arm engageable with and operable to move said pivotedmember, said second relay switch being operable upon closing movement tomove said pivoted member so that said first-named switch and said fourthswitch may open thus de-energizing said first, said second, and saidfourth circuits and energizing said third circuit, and safety meansoperable to move said pivoted member to open said first-named switchupon failure of said second relay switch to close.

5. In a control device, a first circuit and a sec ond circuit, a switchfor controlling said circuits, a relay switch operable to controlenergization of said circuits, a third circuit connected in parallelwith said first circuit, a second relay switch for controlling saidthird circuit, said second relay switch being normally open, a fourthcircuit including a fourth switch, a pivoted member engaging and holdingclosed said first-named switch, said pivoted member eing operable upon apredetermined movement to permit said firstnamed switch to open and toopen said fourth switch, said second relay switch having a pivotedcontact-carrying arm engageable with and operable to move said pivotedmember, said second relay switch being operable upon closing movement tomove said pivoted member so that said first-named switch and said fourthswitch may open thus de-energizing said first, said second, and saidfourth circuits and energizing said third circuit, a bimetal element, anelectric heating coil and circuit for said bimetal element, said bimetalelement being operable upon heating to move said pivoted member, andsaid heating coil and bimetal element being operable as timing means andas safety by moving said pivoted member and thereby opening saidfirst-named switch upon failure of said second relay switch to functionwithin apredetermined time.

6. In a control device, a first circuit and a second circuit, a switchhaving two pairs of contacts for controlling said circuits, a relayswitch having a pair of contacts in said first and said second circuitsand operable to control energization of said circuits, a transformer, athird circuit from said transformer including a third switch andoperable to energize said relay switch, a fourth circuit, a second relayswitch having a pair of contacts in and cont-rolling said fourthcircuit, said second relay switch being normally open, a holding circuitfor said first-named relay 23 switch operable upon closing of saidfirst-named relay switch to hold the same closed independent- 1y of saidthird circuit, a pivoted member engaging and holding closed said firstnamed switch, said pivoted member being operable upon a predeterminedmovement to permit said firstnamed switch to open and to open said thirdswitch, said second relay switch having a pivoted contact-carrying armengageable with and operable to move said pivoted member, said secondrelay switch being operable upon closing movement to move said pivotedmember so that said first-named switch and said third switch may openthus de-energizing said first, said second, and said third circuits andenergizing said fourth circuit, and safety means operable to move saidpivoted member to open said first-named switch upon failure of saidsecond relay switch to close.

7. In a control device, a circuit including a control switch, a secondcircuit in parallel with said first-named circuit and including a secondcontrol switch, said second switch including an arm operable uponclosing movement to open said first-named switch, means for controllingthe energization of said first-named circuit, means for controlling saidcontrol means, safety means operable to open said first-named switchupon failure of said second switch to function, stop means operable toprevent said safety means from returning to its initial state afterfunctioning, a reset mechanism operable upon movement to move said stopmeans to permit said safety means to return to its initial state, andsaid reset mechanism being furtheroperable to actuate said second-namedcontrol means to prevent energization of said first-named circuit.

8. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switchoperable to control said circuits, a relay switch for controllingenergization of said circuits, a third switch for controllingenergization of said relay switch, a second motor circuit, a secondrelay switch for controlling said second motor circuit, a pivoted memberengaging and holding closed said firstnamed switch, said pivoted memberbeing operable upon movement to permit said first-named switch to openand to open said third switch, a holding circuit for said first-namedrelay switch operable to hold the same closed upon opening of said thirdswitch, said second relay switch being operable upon closing movement tomove said pivoted member thereby opening said first-named and said thirdswitches, a bimetal element operable to move against said pivoted memberupon heating, an electric heating coil for said bimetal element, saidheating coil and said bimetal element being operable as safety means tomove said pivoted member to open said first-named and said thirdswitches upon failure of said second relay switch to close within apredetermined time, a flexible stop member operable to (prevent saidbimetal element from returning to its initial position upon cooling, areset member operable upon movement to engage and move said stopmemberthereby to permit said bimetal element to return to its initialposition, and said reset member being further operable upon movement toengage and move said pivoted member.

9. In a control device, a circuit including a switch, a relay switchoperable to control energization of said circuit, a second circuitincluding a third switch, said third switch being initially closed, apivoted member engaging and holding closed said first-named switch, saidpivoted mom-- her being operable upon predetermined movement to permitsaid first-named switch to open and to open said third switch, a thirdcircuit connected in parallel with said first-named circuit, a secondrelay switch having contacts in said third circuit, an electron tube incircuit with and controlling said second relay switch, and said secondrelay switch having a contact carrying pivoted member operable uponmovement to close said contacts in said third circuit and also to engageand move said first-named pivoted member through said predeterminedmovement thereby to open said first-named and said third switches.

10. In a control device, a circuit including a switch, a relay switchoperable to control energization of said circuit, a second circuitincluding a third switch, said third switch being initially closed, apivoted member engaging and holding closed said first-named switch, saidpivoted member being operable upon predetermined movement to permit saidfirst-named switch to open and to. open said third switch, a thirdcircuit connected in parallel with said first-named circuit, a secondrelay switch having contacts in said third circuit, an electron tube incircuit with and controlling said second relay switch, said second relayswitch having a contact carrying pivoted member operable upon movementto close said contacts in said third circuit and also to engage and movesaid first-named pivoted member through said predetermined movementthereby to open said first-named and said third switches, a bimetalelement, an electric heating coil for said bimetal element, and saidbimetal element being operable after heating for a predetermined time tomove said pivoted member the distance necessary to open said first-namedswitch.

11. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch operable to control energization of said circuits, a third switchoperable to control said relay switch, a second motor circuit inparallel with said first motor circuit, a second relay switch havingcontacts in and controlling said second motor circuit, said second relayswitch being normally open, an electron tube in circuit with the coil ofsaid second relay switch and operable to control its operation, apivoted member engaging and holding closed said firstnamed switch, saidpivoted member being operable upon a predetermined movement to permitsaid first-named switch to open, said second relay switch having a[pivoted contact-carrying arm which is operable upon closing movement toenergize said second motor circuit and to engage and move said pivotedmember to open said firstnamed switch, said second relay switch beingoperable upon activation of said electron tube to close thus moving saidpivoted member to open said first-named switch thereby de-energizingsaid motor and ignition circuits and energizing said second motorcircuit, and safety means for de-energizing said motor and ignitioncircuits upon failure of said electron tube to function.

12. In a control device for controlling a burner motor-and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch operable to control energization of said circuits, a third switchoperable to control said relay switch, a second motor circuit inparallel with said first motor circuit. a

second relay switch having contacts in and controlling said second motorcircuit, said second relay switch being normally open, an electron tubein circuit with the coil of said second relay switch and operable tocontrol its operation, a pivoted member engaging and holding closed saidfirst-named switch, said pivoted member being operable upon apredetermined movement to permit said first-named switch to open, saidsecond relay switch having a pivoted contactcarrying arm which isoperable upon closing movement to energize said second motor circuit andto engage and move said pivoted member to open said first named switch,said second relay switch being operable upon activation of said electrontube to close thus moving said pivoted member to open said first namedswitch thereby pie-energizing said motor and ignition circuits andenergizing said second motor circuit, a bimetal element, an electricheating coil for said bimetal element, and said bimetal element beingoperable upon predetermined heating as a safety means to move saidpivoted member to open said first-named switch to deenergize said motorand ignition circuits upon failure of said electron tube to functionwithin a predetermined time.

13. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch operable to control energization of said circuits, a third switchoperable to control said relay switch, a second motor circuit, a secondrelay switch for controlling said second motor circuit, said secondrelay switch being normally open, an electron tube in circuit with thecoil of said second relay switch and operable to control its operation,timing means operable to prevent energization of said firstnamed relayswitch until sufficient time has passed for said electron tube to becomeadequately heated, a pivoted member engaging andholding closed saidfirst-named switch, said pivoted member being operable upon apredetermined movement to permit said first-named switch to open, saidsecond relay switch having a pivoted contact-carrying arm which isoperable upon movement to engage and move said pivoted member, saidsecond relay switch being operable upon activation of said electron tubeto close thus moving said pivoted member so that said first-named switchmay open thereby deenergizing said motor and ignition circuits andenergizing said second motor circuit, a bimetal element, an electricheating coil for said bimetal element, said bimetal element beingoperable upon heating to move said pivoted member, and said bimetalelement being further operable as a safety means to open saidfirst-named switch to de-energize said motor and ignition circuits uponfailure of said electron tube to function within a predetermined time.

14. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch operable to control energization of said circuits, a third switchoperable to control said relay switch, a second motor circuit, a secondrelay switch for controlling said second motor circuit, said secondrelay switch being normally open, an electron tube in circuit with thecoil of said second relay switch and operable to control its operation,timing means operable to prevent energization of said first-named relayswitch until sufiicient time has passed for said electron tube to becomeadequately heated, a pivoted member engaging and holding closed saidfirst-named switch, said pivoted member being operable upon apredetermined movement to permit said firstnamed switch to open, saidsecond relay switch having a pivoted contact-carrying arm which isoperable upon movement to engage and move said pivoted member, saidsecond relay switch being operable upon activation of said electron tubeto close thus moving said pivoted member so that said first-named switchmay open thereby de-energizing said motor and ignition circuits andenergizing said second motor circuit, a bimetal element, an electricheating coil for said bimetal element, said bimetal element beingoperable upon heating to move said pivoted member, said bimetal elementbeing further operable as a safety means to open said first-named switchto de-energize said motor and ignition circuits upon failure of saidelectron tube to function within a predetermined time, a flexible stopmember operable to prevent said bimetal element from returning to itsinitial position upon cooling, a reset member engageable with said stopmember upon movement and operable to move said stop member to permitsaid bimetal element to return to its initial position, and said resetmember being further operable to engage and move said pivoted member toopen said third switch thereby to prevent operation of said controldevice so long as said reset member is in operated position.

15. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch operable to control energization of said circuits, a third switchoperable to control said relay switch, a second motor circuit, a secondrelay switch for controlling said second motor circuit, said secondrelay switch being normally open, an electron tube in circuit with thecoil of said second relay switch and operable to control its operation,an electrical resistor operable to cause a sufiicient voltage droptherethrough to prevent functioning of said first-named relay switch, athermostatic switch responsive to the heat output of said resistor andoperable to close a shunt circuit of less resistance than said resistorafter a predetermined exposure to the heat of said resistor, saidpredetermined exposure being of the same duration as the heating timefor said electron tube, a pivoted member engaging and holding closedsaid first-named switch, said pivoted member being operable upon apredetermined movement to permit said first-named switch to open, saidsecond rela switch having a pivoted contact-carrying arm which isoperable upon movement to engage and move said pivoted member, saidsecond relay switch being operable upon activation of said electron tubeto close thus moving said pivoted member so that said first-named switchmay open thereby de-energizing said motor and ignition circuits andenergizing said second motor circuit, a bimetal element, an electricheating coil for said bimetal element, said bimetal element beingoperable upon heating to move said pivoted member, said bimetal elementbeing further operable as a safety means to open said first-named switchto de-energize said motor and ignition circuits upon failure of saidelectron tube to function within a predetermined time, a flexible stopmember operable to prevent said bimetal element from returning to itsinitial position upon cooling, a reset member engageable with said stopmember upon movement and operable to move said stop member to permitsaid bimetal element to return to its initial position, and said resetmember being further operable to engage and move said pivoted member toopen said third switch thereby to prevent operation of said controldevice so long assaid reset member is in operated position 16. In acontrol device for controlling a burner motor and electric ignitionmeans, a motor circuit and an ignition circuit, a switch having twopairs of contacts and operable to control said circuits, a relay switchhaving a plurality of contacts and operable to control energization ofsaid circuits, a second motor circuit, a second relay switch forcontrolling said second motor circuit, said second relay switch beinginitially open, an electron tube in circuit with and-controlling saidsecond relay switch; a fourth switch having two pairs of contacts, onepair of which are initially closed and one pair initially open; saidlast-named closed contacts being in circuit with the coils of said firstnamed and said second relay switches, said last-named open contactsbeing in circuit with the coil of said second relay switch, a pivotedmember engaging and holding closed said first switch, said pivotedmember being operable upon partial movement to engage said fourth switchto open the closed contacts and to close the open contacts thereof andupon full movement to permit said first switch to open, said secondrelay switch being engageable with said pivoted member on closingmovement, and said second relay switch being responsive to theactivation of said electron tube and upon closing movement beingoperable to move said pivoted member to open said first switch therebyde-energizin said ignition circuit and said first-named motor circuitand energizing said second motor circuit.

17. In a control device for controlling a burner motor and electricignition means, a motor circuit and an ignition circuit, a switch havingtwo pairs of contacts and operable to control said circuits, a relayswitch having a plurality of contacts and operable to controlenergization of said circuits, a second motor circuit, a second relayswitch for controlling said second motor circuit, said second relayswitch being initially open, an electron tube in circuit with andcontrolling said second relay switch; a fourth switch having two pairsof contacts, one pair of which are initially closed and one pairinitially open; said last-named closedcontacts being in circuit with thecoils of said first-named and said second relay switches, saidlast-named open contacts being in circuit with the coil of said secondrelay switch, a pivoted member engaging and holding closed said firstswitch, said pivoted member being operable upon partial movement toengage said fourth switch to open the closed contacts and to close theopen contacts thereof and upon full movement to permit said first switchto open, said second relay switch being engageable with said pivotedmember on closing movement, said second relay switch being responsivetothe activation of said electron tube and upon closing movement beingoperable to move said pivoted member to open said first switch therebyde-energizing said ignition circuit and said first-named motor circuitand energizing said second motor circuit, a bimetal element, an electricheating coil for said bimetal element, said bimetal element beingoperable to move upon heating to engage and move said pivoted member,said bimetal element and heating coil being operable as a timing meansfor actuating said fourth switch to break and to subsequentlyre-establish the circuit through said second relay switch therebydelaying the operation of said second relay switch until sufiicient timehas passed for said electron tube to become adequately heated, and saidbimetal element being further operable as a safety means to move saidpivoted member to open said first switch and de-energize said motor andignition circuits upon failure of activation of said electron tubewithin a predetermined time.

FRED B. AUBERT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,953,425 Miller Apr. 3, 19342,138,244 Raney Nov. 29, 1938 2,185,317 Schmieding Jan. 2, 19402,274,384 Scanlan Feb. 24, 1942 2,345,399 Jones Mar. 28, 1944 2,346,308Isserstedt Apr. 11, 1944 2,351,622 Malone June 20,1944 2,384,372 EatonSept. 4, 1945 2,446,029 Tramontini July 27, 1948

